Glass will break when internal stresses are set up which cause the glass to fracture. These stresses are set up when the temperature of the glass is not uniform from one place to another. So, it is not so much a function of the temperature as the speed of a change in temperature which makes certain parts hotter or cooler than others.

If you heat up a piece of glass very, very slowly, you can bring it to an extremely high temperature without any ill effects. Similarly, if you cool it very slowly there will be no ill effects. However, if you heat it or cool it very quickly, it could break.

That is the general principle. Whether the fracture will occur depends on the glass and the extremes to which the glass is subjected. For example, pyrex is specifically manufactured to withstand sudden, rapid temperature changes or strongly heating one section of the glass but not the rest. Also, modest temperature changes will not create the stress levels needed to cause breakage, and very thin glass will usually cool or heat more evenly since the heat has a chance to dissipate more quickly and evenly.

That does not solve your problem, but it may provide enough guidance in specific situations to avoid problems.

Note that drying has nothing to do with the breakage unless you are drying the glass in very much hotter or cooler conditions than those in which they were washed. The drying process, in itself, is not a factor.

Also, note that using luke warm water followed by hot water will allow the glass to heat up slowly. So, you are on the right track there.

Hope this helps!

PassionForDanceon November 30th, -0001

There’s no fixed answer I’m afraid.

It depends on the type of glass, the thickness of the glass, how the glass is cut, whether there are imperfections in it etc.

In other words, there’s no real way of predicting it, so you’re best not to worry about it unless it happens.

Xfactoron November 30th, -0001

the reason it breaks is because of a large change in temperature, hot water is unlikely to cause any damage. In experience it has to get to a couple of hundred degrees C, and then if you pour cold water over it, it will shatter

SimpleStripeson November 30th, -0001

I depends on a lot of factors. Thin glasses, like wine glasses, are less likely to break than thicker glasses. This is because in thicker glasses, the glass heats up/cools down unevenly, whereas thin glass tends to heat and cool evenly.

Most glass will be fine going straight into hot water straight from the tap. Unless you are putting them from hot water straight into cold water, there shouldn’t be much chance of them breaking. They should be fine going into the fridge after only a few minutes, because the fridge will not cool them down suddenly, but is a more slow cooling process.

Sheepishon November 30th, -0001

above 100*c for all glasses

laird keithon March 1st, 2012

I am concerned about my insulating panels R-9 for my windows. which might cause the glass to break(thermalpane) if the air temperature between the panel and glass gets too hot. Any ideas? thanks laird

Nikkion July 9th, 2014

Please help. I have hung an old mirror backed with wood close to our wood burning stove. It gets rather hot (almost too hot to touch) when we burn the stove in winter. Is it safe to hang the mirror there? It doesn’t heat up very quickly or cool very quickly either as the burner heats and cools depending on how we stack it with wood. Thanks

Share your comment

Name (required)

Mail (required)

Website

About Me

ALES LOMBERGAR is one of the few artisans in Europe who still practice the ancient art of glass acid etching which flourished in the late 19th century. Decorations are applied with resin resists by hand and then exposed to acid baths, with no machinery used. More information here.